/**
 * \* Created with IntelliJ IDEA.
 * \* User: Administrator
 * \* Date: 2022/1/31
 * \* Time: 23:52
 * \* To change this template use File | Settings | File Templates.
 * \* Description:
 * \
 */
class Node{
    public int val;
    public Node next;
    public Node(int val){
        this.val = val;
    }
}
public class MyQueue {
    public Node head;
    public Node last;

    /**
     * 尾插法
     * @param val
     */
    public void offer(int val){
        Node node =new Node(val);
        if(head == null){
            head = node;
            last = node;
        }else {
            last.next = node;
            last = last.next;
        }
    }

    /**
     * 出队
     * @return
     */
    public int poll(){
        if(isEmpty()){
            throw new RuntimeException("队列为空");
        }
        int oldVal = head.val;
        this.head = head.next;
        return oldVal;
    }
    public boolean isEmpty(){
        return this.head == null;
    }
    public int peek(){
        if(isEmpty()){
            throw new RuntimeException("队列为空");
        }
        return head.val;
    }
}
